Cylindrical filters are widely used to filter fluids and comprise a cylindrical housing containing a replaceable filter cartridge, which cartridge comprises a porous cylindrical core member and a pleated filter element surrounding the core. The axes of the pleats are generally parallel to the axis of the core. In normal operation an inlet port communicates with the interior of the housing and an outlet port communicates with the porous axial core member such that the fluid to be filtered is constrained to pass from inlet to outlet through the cylindrical pleated filter element. To ensure that no fluid passes around the ends of the filter element, these are usually sealed into end caps at each end of the cartridge. The end cap through which the outlet port communicates with the axial core member is called the open end cap and the other, which seals off the other end of the core, is called the blind end cap. In some constructions the axial core member has exit ports at both ends as, for example, when a plurality of cartridges are joined together to provide a longer filter device.
The sealing of the ends of the filter element in the end caps is frequently done by placing in the cap a potting compound, which in this context means a material that is liquid under filter cartridge-sealing conditions but solid under normal operating conditions. Typically this will be a molten polymer, a plastisol, a two-part epoxy resin, a wax, a liquid polymer that can quickly be cured to a rigid state, or some such similar material. In one preferred embodiment, the potting compound is in fact the material of the end cap itself. In this embodiment, the surface of the end cap to which the pleats are to be bonded is melted and the pleats are pressed into the molten surface. The end cap is then allowed to cool.
In order for this sealing process to be effective, it is necessary that the end of each pleat be firmly anchored in the potting compound and in practice this means ensuring that all the ends of the pleats penetrate into the compound to approximately equal depth and stay there until the compound solidifies.
In some cases this proves a difficult objective. The viscosity of the potting material may be so high or the rigidity of the filter element so low that the pleats may actually buckle before adequate penetration can be achieved. This problem is exacerbated where the pleats are relatively widely spaced so as to accommodate dirt removed from a filtered fluid.
The present invention provides a means of increasing the ability of a cylindrical pleated filter element to resist buckling when the end is inserted into a potting compound to seal it in place in an end cap of a filtration cartridge. In addition, the extrusion of potting material between the individual pleats is more uniform and controllable.
Another objective is to improve the uniformity of performance of filtration cartridges containing a cylindrical pleated filter element by insuring a reduced rate of filter failure as a result of filtration fluid bypassing the filter element through inadequate end seals.